1. Field of the Invention
The present invention relates to semiconductor devices and methods for manufacturing the semiconductor devices. The present invention particularly relates to a semiconductor device which uses a single crystal semiconductor film formed by a hydrogen ion introduction separation method and a method for manufacturing the same.
2. Description of the Related Art
In recent years, integrated circuits using a silicon-on-insulator (SOI) substrate where a thin single crystal semiconductor film is present over an insulating surface, instead of using a bulk silicon wafer, have been developed. By utilizing characteristics of a thin single crystal silicon layer formed over an insulating film, transistors formed in the integrated circuit can be separated from each other completely. Further, since fully-depleted transistors can be formed, a semiconductor integrated circuit with high added value such as high integration, high speed driving, and low power consumption can be realized.
As a manufacturing method of an SOI substrate, a hydrogen ion introduction separation method in which hydrogen ion introduction and separation are combined is known. A manufacturing method of an SOI substrate using a hydrogen ion introduction separation method is briefly described below. First, by introduction of hydrogen ions into a silicon wafer serving as a substrate for separation by an ion introduction method, an ion-introduced layer is formed at a predetermined depth from the surface. Then, the silicon wafer into which the hydrogen ions are introduced is bonded to another silicon wafer with a silicon oxide film interposed therebetween (bonding). After that, by heat treatment, the ion-introduced layer serves as a cleavage plane, and the silicon wafer for separation, into which the hydrogen ions have been introduced, is separated as a thin film, whereby a single crystal silicon film can be formed over the another silicon wafer. The hydrogen ion introduction separation method is also called a Smart Cut (registered trademark) method.
A method in which a single crystal silicon film is formed over a base substrate made of glass or the like by a hydrogen ion introduction separation method has been proposed (for example, Reference 1: Japanese Published Patent Application No. H11-097379, and Reference 2: Japanese Published Patent Application No. 2005-252244). In Reference 1, a separation plane is mechanically polished in order to remove a defect layer formed by ion introduction or a step of the separation plane, which is several to several tens of nanometers in height. In Reference 2, after the separation step, laser beam irradiation is performed to improve crystal quality of the semiconductor thin film layer and to strongly bond the semiconductor thin film layer and the transparent insulating substrate.